<!DOCTYPE html>
<html>
  <!-- Test: if button has a disabled fieldset ancestor, but is in the first
             legend, it is not barred from constraint validation and should be
             affected by :valid pseudo-class. -->
  <link rel='stylesheet' type='text/css' href='style.css'>
  <body>
    <fieldset disabled>
      <legend>
        <button class='valid'></button>
      </legend>
    </fieldset>
  </body>
</html>
